2-methyl-5-pyrazinoic acid is the key-intermediate for the preparation of ACIPIMOX.RTM. 2-methyl-5-pyrazinoic-1-oxide, an important antihypertensive drug.
From U.K. patent 2,099,820 it is known, how to prepare 2-methyl-5-pyrazinoic acid by condensation of pyruvic aldehyde with diaminodicyanoethylene and subsequent reaction of thus obtained 5-methyl-2,3-dicyanopyrazine with an acid in an aqueous medium.
The reaction between 5-methyl-2,3-dicyanopyrazine with the acid, however, is not selective and gives rise to the formation of equimolecular mixtures of 2-methyl-5-pyrazinoic acid and of 2-methyl-6-pyrazinoic acid, exhibiting the further drawback connected with the separation of said acids.
Moreover from G. B. Barlin "THE PYRAZINES" JOHN WILEY. Ed. page 79 (1982), it is known, how to prepare 2-methyl-5-pyrazinoic acid by oxidation of 2,5-dimethylpyrazine or of 2-methyl-5-oxymethylpyrazine with potassium permanganate.
The above described process, however, proves not to be suitable for an industrial economic production, mostly owing to the considerable amounts of potassium permanganate, which need to be used (from 1 to 2 moles of KMnO.sub.4 per mole of substrate) and to the problems connected with the separation and disposal of large amounts of wastes.
Moreover, the reaction between 2,5-dimethylpyrazine with KMnO.sub.4 is not selective and gives rise to the formation of considerable amounts of 2,5-dicarboxypyrazine as well.
From J. Kaulen et al.--"Synthesis", 513-516 (1979) it is also known, how to electrochemically oxidize primary alcohols on NiO(OH) nickel oxide-hydroxide anode.